Ammonium thiocyanate manufacture



Sept. 2, 1958 H. SUTHERLAND ETAL 2,850,356

AMMONIUM THIOCYANATE MANUFACTURE 4 Y l H25 T0 SULFUR RECOVERY /3 L-Hgo FEED AUEOUS NH4 SON DE UUDGUUU 0 OOOLER .Mmmm on a INVENToRs. HUNT SUTHERLAND, BY w/LL/AM D. @ERSU/wn'.

A 7` TRNE Y.

2,859,356 leuter-tred Sept. 2, 1958 ice MMNllUh/i THSCYMWA'I'E MANUFACTURE i-lunt Sutherland, Springdale, and William D. Gersumir' Greenwich, Conn., assigner-s to American Cyananurl Company, New York, N. 'V a corporation of Maine This iuvenion relates to a novel preparation of ammonium thiocyauate More particularly it relates to the preparation of ammonium thiocyanate by causing ammonia and carbon disulfidein an aqueous medium to react under substantially atmospheric pressure.

the past, any process involving the reaction of ammonia and carbon disuliide in an aqueous medium to yield ammonium thiocyanate could be performed under moderately high superatmospheric pressures. Such pressures were in the range of from about S() p. s. i. to i() p. s. i. However, the use of such pressures was not wholly satisfactory for the reason that expensive pressure equipment was required. Also, special sat'ety precautions had to be taken in utilizing pressure equipment.

It is, therefore, a principal obiect or the present invention to provide a process for conducting the reaction or" ammonia and carbon disuhide in an aqueous medium at substantially atmospheric pressure. lt is a further object of the invention to provide such a process in which the use or" pressure equipment can be substantially eliminated.

These, and other objects, are attained in a surprisingly expeditiously and simple manner. it has been found that ammonia and carbon disuliide can be advantageously reacted in an aqueous medium provided the latter contains suiicient ammonium thiocyanate. Ey this simple discovery, it has been found that it is unnecessary to employ superatmospneric pressures to obtain satisfactory yields of ammonium thiocyauate of good quality.

According to the present invention, at least two mois ot' ammonia and about one mol of carbon disulide are reacted under substantially ambient conditions in the presence of an aqueous ammonium thiocyanate medium. ln general, the latter contains from about to about 50% ol' ammonium thiocyanate by weight. About 30% to about 40% is a good general practice. Once the medium is established, the carbon disulfide and ammonia are fed tbereinto, either simultaneously or in separate streams. The reaction is carried out in a vessel suitably equipped with heating means. The Vessel itself is so equipped that it can be heated in such manner as to provide a controlled temperature gradation.

The invention will be more readily understood from the following more detailed description of a preferred embodiment of the invention and from the accompanying drawing wherein:

The drawing is a schematic ow diagram for effecting reaction between carbon disullide and ammonia subntially atmospheric pressure. "ihis flow diagram constitutes a preferred embodiment of the invention,

Rei rring to the drawing, 1 represents a reaction tower. lt is lilled with conventional packing, such as porous chips or Raschig rings. For simplicity of explanation, the tower is subdivided into three zones, all designated by brackets, namely an upper zone 2, an intermediate or central zone 3, and a lower zone 4i. ln the upper zone 2, an average temperature of about 35 C.

is maintained, although a temperature rmge of from about 30 C. to about 40 C. is provided. This zone, otherwise termed the ammonia absorption zone, insures the removal of hydrogen sulfide as a gas and allows for ammonia absorption into an aqueous ammonium thiocyanate solution which is introduced into the topmost section of that zone. The latter solution also serves to c 'sa the liquid medium of the central zone. The central or middle zone S is maintained at from above about 40 C. to below about 70 C. with an average temperature of about 55 C. Carbon disulfide and ammonia are introduced into this zone through lines 5 and 6 respectively. iteaction occurs in the liquid phase with the attendant ascent of gaseous hydrogen sulde and gaseous unreacted ammonia. The latter ammonia is returned. to the reaction zone, however, when it is liqueiied in the ammonia absorption zone 2. in the lower zone 4t, a temperature of from about C. to about 95 C. with an average temperature of about C. is provided. This zone substantially prevents any unreacted liquid ammonia from being withdrawn along with product ammonium thiocyanate. Ammonia in the latter product is evaporated into the middle zone 3 where it can be reacted with carbon disulfide.

For the size of the tower, the flows of 'mcoming carbon disulfide and ammonia are so regulated as to insure reaction in the reaction zone. Additionally, aqueous ammonium thiocyanate is introduced into the upper zone 2 at a rate so as to permit it to maintain a liquid level within the reaction zene for good practice. However, the so-introduced ammonium thiocyanate may be introduced at a rate to ll the ammonia absorption zone either partially or substantially completely, although this latter procedure is not the best practice for effecting ammonia absorption in that zone.

Product ammonium thiocyanate is withdrawn through line 7. lt is divided into two portions at valve 8. One portion is withdrawn at line 9 and another is recycled to the tower ll through lines 10V and 11 respectively. However, prior to its entry into the tower, the returned ammonium thiocyanate is first passed through a heat eX- changer 12 where it is cooled. The -so-cooled ammonium thiocyanate is diluted before introduction into the upper zone, by admixing water therewith. The water is fed as shown through line i3. As indicated above, gaseous hydrogen sulfide is withdrawn ifrom the upper zone 2 and is led through line i4 to a sulfur recovery plant.

The average temperature in each zone of the tower is maintained by techniques well known to the art. For example, by properly spacing heating and cooling coils (not shown) which envelop the tower, the desired temperature yrange can be easily obtained in each zone.

Although a reaction tower having packing has been described above, any mechanical equivalent thereof can be employed in the successful practice of the present invention. For example, a fractionating column of bubblecap plate design is within our purview and contemplation.

in a typical run, the apparatus or the drawing is simply utilized by permitting separate streams of liquid carbon disulde and liquid ammonia to be continuously fed into the reaction zone. Sao-introduced reactants may be in the gaseous form, if desired, although either gaseous or liquid reactants are added with advantage. A liquid level is maintained in the reaction zone which is maintained at an average temperature of about 55 C. During reaction, gaseous hydrogen sulfide and unreacted arnmonia rise into the upper zone maintained at an average temperature of about 35 C. Gaseous hydrogen sulde is ed, while gaseous ammonia is condensed and is returned to the reaction zone. ln the meantime, a 3% aqueous ammonium thiocyanate which has been previously cooled to about the average temperature in the upper zone is introduced in the upper section of the zone and trickles or otherwise flows into the reaction zone. Product ammonium thiocyanate accumulates in the bottom zone and ris continuously withdrawn. However, prior, to its withdrawal, any accumulated ammonia is evaporated since the average temperature of the bottom zone is maintained at about 80 C. A 50% concentrated solution of product ammonium thiocyanate, substantially free from ammonia and of course hydrogen sulde, is withdrawn from the bottom section of the bottom zone. A portion of the latter is cooled and diluted with water. So-diluted ammonium thiocyanate which provides the reaction menstruum is reintroduced into the uppermost portion of the tower.

Although the process of the present invention has been described with reference to the use of atmospheric pressure during reaction, it is an advantage of the present invention that in addition to the use of ammonium thiocyanate, a slight elevated pressure of from to l0 p. s. i. g. can be employed. In such manner, ammonium thiocyanate produced will be swiftly eliminated from the system and recovered. It is also within the purview of the invention that the aforedescribed process may be Vcaused to operate either 4batch-Wise as well as continu ously.

We claim: 1. A process for preparing ammonium thiocyanate which comprises the steps of: feeding at least two mols of ammonia and one mol of carbon disulide into the central zone of a reactor maintained under ambient conditions and comprising an upper zone, central zone and of from about C. to about 40 C.;and eliminating hydrogen suliide fromY said zone.

2. A continuous process for preparing ammonium thiocyanate which comprises the steps of: providing a packed tower comprising an upper zone, a central zone and a lower zone, progressively heating each zone While maintaining an average temperature of about (a) C. in the upper zone of said tower, (b) about C. in the central zone and (c) about 80 C. in the lower zone;

introducing aqueous ammonium thiocyanate into the up- Y permost portion of said upper zone; establishing said aqueous ammonium thiocyanate menstruum in the central zone; feeding carbon disulde and ammonia into said middle zone, removing gaseous hydrogen sulfide from theupper zone; absorbing ascending gaseous ammonia intoy said introduced aqueous ammonium thiocyanate located inthe upper zone; returning said unreacted absorbed ammonia to the central or reaction zone; evaporating accumulated liquid ammonia in said lower zone; returning the latter ammonia to the central zone; and withdrawing ammonium thiocyanate substantially Vfree from ammonia from the lower zone.

3. A process according to claim 2 in which the aqueous ammonium thiocyanate is introduced into the uppermost section of the upper zone at a concentration of from Vabout 20% to 50%. Y

. 4. A process according to claim 2 Iin which the aqueous ammonium thiocyanate is introduced into Ithe uppermost section of the upper zone at a concentration of about 30%.

5. A process according to claim 2 in which the aqueous ammonium -thiocyanate is introduced into the uppermost lower zone; maintaining the central zone at a temperature of above about 40 C. and below about 70 C.; establishing in said .central zone an aqueous medium containing of from about 20% to about 50% by weight of ammonium thiocyanate; withdrawing ammonium thiocyanate substantially free from ammonia from the lowermost portion of the bottomzone maintained at a temperature of from above about C. and about 95 C.; diluting a portion of withdrawn ammonium thiocyanate with water; cooling the latter solution; recycling the cooled diluted ammonium thiocyanate to the uppermost portion of the upper zone maintained at a temperature section of the upper zone at a temperature corresponding f to the average temperature of the said zone.

.6. A process according to claim 2 in which the rates of the respective feeds are so correlated as to maintain the predetermined temperature conditions in each of the said zones. n

References Cited in the lile of this Vpatent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,850,356 September 2, 1958 Hunt Sutherland et al.

s n the printed specification It s herab?? certified that error appear that the seid Letters of the above numbered patent requiring correction and Patent should read as corrected below.

Comm '2, line 71, for "3%" read 30% Signed and sealed this 13th dey of January 1959,

(SEAL) Attest:

KARL -AXLINE 4 ROBERT C. WATSON Commissioner of Patents ,meeting officer 

2. A CONTINUOUS PROCESS FOR PREPARING AMMONIUM THIOCYANATE WHICH COMPRISES THE STEPS OF: PROVIDING A PACKED TOWER COMPRISING AN UPPER ZONE, A CENTRAL ZONE AND A LOWER ZONE, PROGRESSIVELY HEATING EACH ZONE WHILE MAINTAINING AN AVERAGE TEMPERATURE OF ABOUT (A) 35*C. IN THE UPPER ZONE OF SAID TOWER, (B) ABOUT 55*C. IN THE CENTRAL ZONE AND (C) ABOUT 80*C. IN THE LOWER ZONE; INTRODUCING AQUEOUS AMMONIUM THIOCYANATE INTO THE UPPERMOST PORTION OF SAID UPPER ZONE; ESTABLISHING SAID AQUEOUS AMMONIUM THIOCYANATE MENSTRUUM IN THE CENTRAL ZONE; FEEDING CARBON DISULFIDE AND AMMONIA INTO SAID MIDDLE ZONE, REMOVING GASEOUS HYDROGEN SULFIDE FROM THE UPPER ZONE; ABSORBING ASCENDING GASEOUS AMMONIA INTO SAID INTRODUCED AQUEOUS AMMONIUM THIOCYANATE LOCATED IN THE UPPER ZONE; RETURNING SAID UNREACTED ABSORBED AMMONIA TO THE CENTRAL OR REACTION ZONE; EVAPORATING ACCUMULATED LIQUID AMMONIA IN SAID LOWER ZONE; RETURNING THE LATTER AMMONIA TO THE CENTRAL ZONE; AND WITHDRAWING AMMONIUM THIOCYANATE SUBSTANTIALLY FREE FROM AMMONIA FROM THE LOWER ZONE. 